Description: This application proposes a prospective 24-month cohort study to describe referral practices to be conducted in the Ambulatory Sentinel Practice Network (ASPN). The investigators will evaluate information on referred and non-referred patients during 25 consecutive practice days for 150 family physicians in the U.S. Days six to 15 will be the index cases for the remainder of the study. Data also will be tracked on patients who see the physicians on days 16 through 25. The study will include an estimated 90,000 offices and 6,000 referrals with follow-up measurements obtained from 2,000 referred patients and the referring physicians three months after the patients' next visits. The study has three aims, one being primarily descriptive and two relating to an analysis of the study data with four hypotheses to be tested. Aims of this study are: (1) to characterize referral patterns by primary care physicians, by type of referral and by specialty for referral; (2) to determine how managed care financial incentives and organizational controls influence primary care physicians referral practices; and (3) to assess how alternative financing and organizational arrangements affect coordination of care and patient outcomes. The investigators outline the specific variables and analysis that will be used for each aim. Study variables include those related to managed care, immediate and intermediate patient outcomes, coordination of referral, and the quality of primary care delivered.